The goal of this K01 proposal is to develop a culturally tailored nutrition communication intervention for primary prevention of breast cancer among bicultural Latinas. The overarching goal of the study is to advance understanding of how communication and acculturation processes influence cancer risk behaviors in order to design effective culturally tailored interventions to reduce cancer risk behaviors. This approach is particularly relevant when considering research on the health of the population of CA's San Joaquin Valley (SJV). A vast, largely rural region that produces over half of the nation's fruit, nuts, and vegetables, SJV is 50% Latino, mostly of Mexican origin6. The SJV has a very diverse Latino population: 25% are foreign-born, and their primary language may be an indigenous Mexican language rather than Spanish, while 75% are native-born U.S. citizens, who possess varied fluency in English abilities and whose families may include both legal and undocumented immigrants. The linguistic and acculturative diversity of this population poses new challenges for understanding how to design effective behavior change interventions. Most community-based interventions with Latinos have focused on those who speak Spanish exclusively, limiting our understanding of how acculturation and linguistic diversity impact communication intervention design and effectiveness. mHealth strategies offer a way of delivering interventions that are not only culturally appropriate for Latinos across the acculturation spectrum, but also appropriate for primary cancer prevention among young adults who are eager adopters of technology. This study aims to fill the knowledge gaps through a research plan designed around three sequential aims employing mixed methods for message testing and community intervention research. In Aim 1, we will conduct semi-structured interviews with SJV Latinas (N=25) to explore factors that influence diet and food preparation behaviors as well as barriers and facilitators to the adoption of healthier diets. Results will inform the content categories for message tailoring, the structure of the messages, and the means of dissemination. In Aim 2, we will use the findings from Aim 1 to build and test a library of messages that are culturally appropriate for bicultural Latinas using focus groups and cognitive interviews. Aim 3 is the design, pilot test, and evaluation of an intervention to improve diet behaviors. The intervention consists of a series of culturally appropriate messages, developed in Aim 2, tailored to each participant's needs and preferences, to be disseminated via mobile phone over a 4-week period. We will evaluate preliminary outcomes (e.g., usage and feedback about the intervention and changes in knowledge, attitudes, and behavioral intentions) at four different times. We will determine preliminary estimates of effect size for behavioral outcomes (consumption of dietary fat, fruits and vegetables), based on two post-intervention data collections. We will additionally evaluate the feasibility, acceptability, and sustainability in order to refine the intervention for a future larger randomized controlled trial, to be proposed in an R01 application before the end of this award.